Phonon sideband

There are three main EA spectral features in the energy range of band I a derivative-like feature with zero-crossing at 2.29 eV, followed by vibrational features, and an induced absorption band between 2.9 and 3.2 eV. The features below 2.5 eV are the results of a redshifted 1 Bu exciton energy, and its phonon sidebands (Stark shift). These features are more easily observed in EA than in absorp-... 

A schematic energy-level diagram of Cr3+ and Tm3+ in YAG together with the luminescence and absorption spectra of Cr3+ are shown in fig. 18. Three primary Cr3+ - Tm3+ energy transfer pathways can be identified thermally activated energy transfer from the 4T2 state (4T2 ET), thermally activated energy transfer from the 2E anti-Stokes phonon sidebands (2E anti-Stokes ET), and temperature-independent energy transfer from the zero phonon and Stokes phonon sidebands of the 2E state (2E Stokes ET). 

The temperature dependence of the energy transfer rate Wda is related to a changing occupation of the 2E anti-Stokes phonon sidebands and the 4T2 state. On the contrary, pressure significantly increases the energy separation A between the 4T2 and 2E states, whereas the energy of the zero phonon and the vibronic 2E -> 4A2 transitions of Cr3+ change only weakly with pressure. Thus, pressure almost solely influences the occupation of the 4T2 state and with it its contribution to the energy transfer rate, but does not affect the other contributions connected with the 2E state. 

Bai et al. (2005) observed a phonon sideband with a frequency shift of 40-50 cm-1 located on the low-energy side of the 5Do <- 7Fo zero-phonon line (ZPL) in the 77 K excitation spectrum of Eu3+ Y203 NTs and NWs. However, vibronic sidebands generally appears at the high-energy side of the ZPL in the low-temperature excitation spectra since the vibronic transition involving the creation of a phonon with the annihilation of a photon is much more favored than the annihilation of a phonon at low temperature. The origin of this anomaly sideband remains unknown. 

Figure 2.12. Real and imaginary parts of the dielectric permittivity e(co) around the fe-polarized 0-0 transition, obtained from Kramers-Kronig analysis of rellectivity spectra at temperature ranging from 7 to 77 K. The arrow on the r. curves indicates the point where e = 0. We note the stepwise threshold of the 46-cm-1 phonon sideband (a). At higher temperatures (b-h) it broadens to give the smooth asymmetrical absorption curve at SO K (g).

Z(a)) = <5(a>) + j y(co) is the excitonic self-energy and satisfies KK relations e0 and A assume the previous values. The derived variations of <5(co) and y(ai) are presented in Fig. 2.13. We notice that (5(w), though fairly weak throughout the 0-0 region, reaches values of 20cm" around the phonon sideband, and should therefore be included in quantitative estimations of y(cu).95 We find that y(co) increases between co0 and co0 + 46 cm" crosses a stepwise threshold at a>0 + 46 cm" and then steadily grows to a>0 + 394 cm", where a vibronic study56 would be better suited than the parametrization (2.125). 

In the first-order phonon sidebands of the EA spectrum there are four features (arrows in Fig. 6(a)) that correspond to the maxima of the absorption spectrum. In our case, these features in the EA spectrum are zero-crossing points or points associated with the largest slope in the regions of fall-off of the absorption coefficient. These features correlate very well with the four strong peaks in the S5mmetrized LVDS projected onto displacements with Aj- and E-symmetries of the ions of two coordination spheres around a Ni impurity (see Fig. 6(b)). These peaks correspond to the localized vibrations induced by the Ni impurity. 

Figure 2 Schematic of the electronic absorption spectrum of a single chromophoric site in a condensed phase host environment at low temperatures. An extremely sharp electronic origin, exhibiting a radiatively limited linewidth is accompanied by a phonon sideband with vibrational sidelines. A second electronic excited state lies at higher energies. Vibrational sidelines and the second electronic excited state are lifetime broadened by rapid radiationless deactivation processes...

Fig. 18.8 The emission spectrum observed following excitation of Azulene in Naphthalene matrix at T = 2 K. Upper panel emission following excitation into the zero phonon line. Lower panel— emission following excitation into the phonon sideband, 30 cnr above the zero-phonon line. (Fig. 1 of R. M. Hochstrasser and C. A. Nyi, J. Chem. Phys. 70, 1112 (1979).)...

Fig. 11.1. Absorption (right side) and emission spectrum (left side) of a 170 micron thick crystal at 2 K. The arrows at the right-hand side indicate phonon sidebands in the absorption spectrum. The pattern is symmetrically repeated at the low energy side of the zero-phonon line. Reprinted with permission from Rose et al. (23). Copyright Elsevier (1984).

When the first term is nonzero the electronic transition is allowed by a particular mechanism, whereas it is forbidden when zero. It contributes mainly zero phonon line intensity when the shift in equilibrium positions of the nuclei between the two states can be ignored, so that (Zfk Xin)t 0 only for the k=n case in Eq. (17). The second and third terms contribute mainly one-phonon sideband vibronic intensity to the transition. (i/q Me i/r ) 2 is given by [68]... 

Table 4 k=0 Selection rules for one-phonon sideband structure of the i—>f transition in the EDV spectra of octahedral symmetry compounds (from [110]). The M2ALnX6 unit cell group modes contain Tiu+t2u, but not eu or ai ... 

The very first laser, the ruby laser, belongs to the family of the transition metal ion lasers. However, its wavelength is fixed.Its lower lasing state is the ground state, the orbital momentum of which is quenched by the crystal field. There is no direct coupling of the lattice vibrations to this ground state, i.e. no phonon sideband can occur. 

The final process shown in Fig. 9 is photon avalanche (PA), which presents some unusual characteristics [133, 134] in that nomesonant GSA leads to strong upcon-verted emission. In Fig. 9, C is not an electronic energy level. The absorption transition A C is weak since it is due to such reasons as phonon sideband or defect absorption. Level B is then populated by nomadiative decay. The laser pump firequency matches the ESA B D. Then, this can be followed by emission from D, or the cross-relaxation process ... 

Miyakawa T, Dexter DL (1970) Phonon sidebands, multiphonon relaxation of excited states, and phonon-assisted energy transfer between ions in solids. Phys Rev B 1 2961... 

Miyakawa and Dexter (1971) showed that it is still legitimate to write the probability of energy transfer in the form of eq. (142), where p(E) is taken as Ssa, the overlap of the lineshape functions for emission in ion S and absorption of ion A, including the phonon sidebands in the lineshape. It is necessary to consider each partial overlap between the m-phonon emission line shape of ion S and the n-phonon absorption lineshape of ion A. This mathematical assumption has gained experimental credibility through the existence of multiphonon sidebands for trivalent R ions which, in a case of very weak electron-phonon coupling (Auzel 1976) could not be observed directly by usual spectroscopy. 

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